Where can i find this?

No. Im attempting (maybe failing) to make my shower area as waterproof as possible because i really dont want to rip out my tub to fix moldy drywall after we do this remodel. I dont honestly think my structure can support ceramic tile which is why im not doing it. Im using a 3 piece interlocking acrylic surround and my mom saw this and said if we put it over the cement board or drywall that it would prevent water from getting behind the surround. Im not stupid enough to think that just the surround can keep water at bay. If we put this behind the surround, shouldnt it keep the water from gaining access to the cement board or drywall?

Im not sure what would be the better bargain, im still pricing the drywall and cement board.

Where can i find this?

If you buy a nail on enclosure it will be at least 3 times as thick and no drywall is even need behind it.
Even a cheap glued on enclosure glued over green board installed right is not going to leak.
You looking at spendiing a whole lot of money and time on something that's not needed.

Where can i find this?

Not worried about it leaking. Im worried about water getting behind the surround from splash-over. The bathroom is 7' tall at the bathtub spot, my future husband is 6'4". If the surround only goes up as high as the original did, then water will splash off of his head and hit the wall. Thats what im worried about. i know the enclosure wont leak.

Where can i find this?

I am 6'-4", and with our shower head placed high on the wall, never have issues with water getting behind the Green board. You really have to be splashing around, or leaving the water pointing at the wall, for it to do anything.

Where can i find this?

The thing with the Shluter system is It"s guaranteed to be water proof, not just water resistant. My local big box store doesn't carry the Kerdi just Ditra. You may have to go to a tile store to find the kerdi.

Where can i find this?

For what it's worth, at 6' 6", I don't have any issues you're talking about. There is mold and mildew resistant drywall which will be a good alternative in my opinion. Any shower surround, if installed properly will do its job with wonders. While there is potential for moisture to get on the drywall above the shower head theoretically, it should be a non issue. Top of the surround should be caulked to prevent such things from getting behind.

Where can i find this?

You might consider covering the space between the suround and the ceiling with ceramic tile. Shouldn't take more than maybe three rows. I did it in one of my houses, more for a nice accent than anything else. I am also 6' 6", and have never had an issue with splashover either.